Low‐level infection of parasitic copepods on Rainbow Trout does not affect vulnerability to angling or short‐term survival following catch‐and‐release angling

Abstract

AbstractObjectiveParasitic copepods, or “gill lice,” can harm fish hosts, resulting in reductions in fitness and increased probability of mortality. The purpose of our study was to determine the effect of Salmincola californiensis on the vulnerability of Rainbow Trout Oncorhynchus mykiss to recreational angling and short‐term survival after being caught and released.MethodsWe compared the prevalence and intensity of infection of S. californiensis on Rainbow Trout that were caught while angling and with a backpack electrofisher in May and October 2020 in Birch Creek, Idaho. In October, we also conducted a stress test (air‐exposure treatment) on trout that were caught by angling to determine the effects of parasitic copepods on the short‐term survival of Rainbow Trout in a catch‐and‐release fishery.ResultInfection with S. californiensis did not influence the vulnerability of Rainbow Trout to angling. After adjusting for sample size and size distribution, the prevalence of infection in May was 48.3% for Rainbow Trout that were caught while electrofishing and 49.3% for Rainbow Trout that were caught while angling. In October, the prevalence of infection was 41.2% for Rainbow Trout that were caught while electrofishing and 41.8% for Rainbow Trout that were caught while angling. We did not find a difference in short‐term survival rates for infected and uninfected Rainbow Trout after the stress test (4–7 days after the test).ConclusionWe did not observe consequences of infection by parasitic copepods on vulnerability to angling or short‐term survival of Rainbow Trout in Birch Creek. However, the conditions (low‐level of infection and relatively small fish) may not have been conducive to detecting differences in the performance metrics; further testing at higher intensity of infection and with larger fish may uncover the negative effects of parasitic copepods on Rainbow Trout.